Alcohol is classified as a central nervous system depressant. The mechanisms that underlie this alcohol-induced depression of nervous system excitability, however, are poorly understood. This project investigated the intrinsic mechanisms involved in the regulation of nerve cell excitability and the effects of ethanol on those mechanisms. To identify neurons that have been isolated for patch-clamp recording, neurons were retrogradely labeled in vivo using fluorescent dyes. Fast blue was found to be a suitable tracer for studying the electrical properties of identified neurons after isolation in vitro. To study the regulation of excitability mechanisms, neurons were dissociated from the dorsal root ganglia (DRG) of adult rat and maintained for over 3 weeks in tissue culture without serum or added growth factors. Under these conditions, the Na currents of all neurons studied were sensitive to tetrodotoxin (TTX). By contrast, in neurons freshly isolated or cultured in the presence of serum and nerve growth factor (NGF), both TTX-sensitive and TTX- insensitive Na currents were observed. The effect of NGF was tested by culturing adult rat DRG neurons in the presence or absence of NGF in a defined medium without background cells. In the absence of NGF, only TTX- sensitive Na currents were observed; however, in the presence of NGF, both TTX-sensitive and TTX-insensitive Na currents were elicited. The results suggest that NGF may regulate the expression of voltage-gated ion channels in adult mammalian neurons. In addition, several types of voltage-gated ion channels have been characterized in adult mammalian neurons. These include: TTX-sensitive and TTX-insensitive Na channels; transient (T type) and long-lasting (L type) Ca channels; and transient (A), sustained (delayed rectifier), calcium-activated (C) and muscarine inhibited (M) K channels. The effect of ethanol was tested on these voltage-gated ion channels in different types of mammalian neurons and it was found to have little or no effect in a pharmacologic concentration range (100 mM or less).